The electrical conductivity (.sigma.) of most organic materials at room temperature is quite small (.sigma.&lt;10.sup.-10 ohm.sup.-1 cm.sup.-1). Over the last two decades, the synthesis of organic molecules with electrical properties approaching those of metals have been the focus of considerable attention. Because organic polymers generally have elasticity, strength and plasticity, they offer significant advantages over non-polymeric materials in the manufacture of electronic materials. Macromolecular substances can now be tailored to perform as semiconductors or even as true organic metals.
The field of organic metals is dominated by two types of molecular structures: linearly conjugated .pi.-systems and charge-transfer complexes which form stacks of .pi.-systems in the solid state. In the former systems, electrons move rapidly along a partially oxidized or reduced molecular chain. Examples of linear .pi.-conjugated systems are the heteroaromatic polymers such as polypyrroles, polythiophenes, polyanilines, polyacetylenes and polyarylenes. In charge-transfer complexes, electrons move along a partially oxidized or reduced stack of molecules. Examples of this type of conductive polymer include stacks of 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anions stabilized by polycations. See, R. I. Stankovic et al., Eur. Polym. J., 26, 675 (1990). In either case, the electrical, optical and magnetic properties are a complex function of the solid state structure, and efforts have been made to prepare and study model compounds for these systems, primarily in solution.
The high electrical conductivity of heteroaromatic polymers has spurred interest in the use of these materials in novel electronic and chemical applications. See D. Jean et al., Top. Curr. Science, 256, 1662 (1992); J. Heinze, Top. Curr. Chem., 152, 1 (1990); N. C. Billingham et al., Adv. Polym. Sci., 90, 1 (1989); and A. J. Heeger et al., Synth. Metals, 41, 1027 (1991). Prototype designs of flexible light-emitting diodes, molecular transistors, light battery electrodes, electrochemical displays, electrodes for in vivo drug delivery and anticorrosion films, in which a conductive polymer is the active element, have been realized during the past decade. See, L. L. Miller et al. (U.S. Pat. No. 4,585,652) and S. Li et al., Science, 259, 957 (1993) and references cited therein. However, most electrically conductive polymers have undesirable characteristics such as insolubility, intractability, low resistance to water or heat, poor processibility or, in some cases, low molecular weights. These disadvantages prevent the use of conventional polymer-processing techniques to shape these materials into desired structures. With respect to conductive polymer fibers, processing methods have been disclosed which require multistep chemical or mechanical procedures. For example, see D. D. C. Bradley et al., Synth. Metals, 17, 473 (1987); J. M. Machado et al., Polymer, 30, 1992 (1989); and P. Smith et al., Polymer, 33, 1102 (1992).
Therefore, a continuing need exists for simplified methods which yield polymer fibers which exhibit a desirable spectrum of mechanical properties while retaining high electrical conductivity.